ADHD refers clinically to a relatively common syndrome (epidemiologic studies have suggested that the prevalence of ADHD among the general population is between 2-10%). ADHD begins in childhood and typically remits by adulthood (Szatmari Child Adolesc. Psychiat. Clin. North Am. 1982, 1, 361-371). ADHD is clinically characterised by inattention (e.g. failure to give close attention, difficulties in sustaining attention, difficulties in organising tasks and activities and easily distracted by extraneous stimuli), hyperactivity (e.g. difficulties in remaining seated, excessive motor activity in inappropriate situations, the patient acts as if “driven by a motor”) and impulsivity (e.g. difficulties in awaiting turn, answer questions before they have been completed and often interrupts or intrudes ongoing conversation; American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), 1994).
Twin studies of ADHD have indicated that around 80% of the etiology of ADHD is attributed to genetic factors (Gjone et al. J. Am. Acad. Child Adolesc. Psychiat. 1996, 35, 588-596). Although, the strong genetic component of the disease, the patophysiology of ADHD, is currently not known. Cognitive, physiological and imaging studies indicate that ADHD might involve a dysfunction of the cortical inhibition of subcortical structures (Faraone and Biederman Neurobiology of Mental Illness, eds: Charney, Nestler and Bunney, Oxford University Press, 1999, 60, 788-801). Both the tentative involvement of cortical areas and the well-recognised effects of stimulant medication on monoamine metabolism suggest that ADHD might be associated with malfunctioning of the monoaminergic pathways projecting to the cortex (including the dopaminergic and the serotonergic systems).
A very useful animal model of ADHD is the DAT knock-out (KO) mice (Gainetdinov et al. Science 1999, 283, 397-401). These mice lack the gene encoding the dopamine transporter (DAT) and exhibit pronounced hyperactivity, which can be reversed by psychostimulants such as methylphenidate and amphetamine, drugs frequently used in the pharmacotherapy of ADHD. Interestingly, compounds that increase serotonergic neurotransmission such as the selective serotonin re-uptake inhibitor fluoxetine, the serotonin receptor agonist quipazine as well as the serotonin precursors 5-hydroxytryptophan and L-tryptophan were also found to counteract the hyperactivity in these DAT-KO mice (Gainetdinov et al. Science 1999, 283, 397-401).
Several clinical studies have found that tricyclic antidepressant drugs, which block the serotonin transporter, are effective in the treatment of ADHD (Spencer et al. J. Am. Acad. Child Adolesc. Psychiat. 1996, 35, 409432; Wilens et al. J. Clin. Psychopharmacol. 1995, 15, 270-279). Furthermore, there is also evidence that the selective serotonin re-uptake inhibitor fluoxetine is effective in reducing symptoms of ADHD (Barrickman et al. J. Am. Acad. Child Adolesc. Psychiat. 1991, 30, 762-767).
However, psychostimulants, particularly methylphenidate and dextroamphetamine, have been and continue to be the drugs of choice in treating patients with ADHD (Faraone and Biederman, In: Neurobiology of Mental Illness, eds: Charney, Nestler and Bunney, Oxford University Press, 1999, 60, 788-801). Although psychostimulants appear effective, there are a number of problems associated with their use in the treatment of ADHD patients. For example, some patients do not respond at all or only partially to treatment. Furthermore, adverse effects such as insomnia, decreased appetite, irritability, tics and depressive symptoms after long-term treatment are relatively frequent in ADHD patients treated with psychostimulants.
Consequently, there is still a large unmet need for efficient and better tolerated drugs for the treatment of this condition.
WO 98/28293 describes a series of substituted indane and dihydroindole compounds having effect at dopamine D4 receptors. The compounds described are considered useful for the treatment of a range of psychiatric and neurological disorders, including the positive and negative symptoms of schizophrenia, other psychoses, anxiety disorder, such as generalised anxiety disorder, panic disorder and obsessive compulsive disorder, depression, alcohol abuse, impulse control disorders, aggression, side effects induced by conventional antipsychotic agents, ischaemic disease states, migraine, senile dementia, cardiovascular disorders and for the improvement of sleep.
It has now, surprisingly, been found that a compound of WO 98/28293, namely 3-[1-[2-(1-acetyl-2,3-dihydro-1H-indol-3-yl)ethyl]-1,2,3,6-tetrahydropyridin-4-yl]-6-chloro-1H-indole having the formula
which is described herein as a potent dopamine D4 ligand, may be particularly useful in the treatment of attention deficit hyperactivity disorder.